The present invention relates to a liquid crystal display (LCD) and, in particular, to an active matrix LCD integrated with a pen input apparatus. Description of the Related Art
FIG. 1 is a cross-sectional view briefly showing structure of an example of an active matrix LCD of a twisted nematic (TN) mode driven or addressed by thin-film transistors (TFTs). As can be seen from FIG. 1, the active matrix LCD of the prior art includes a substrate 10a with pixel electrodes 8 and a substrate 10b with a common electrode 6. Each glass substrate 10a, 10b has a thickness of about 0.6 millimeter (mm) to 1.1 mm.
Disposed on the glass substrate 10b is a common electrode layer 6. For a color panel, there is further arranged a color filters. On the other side, there are disposed on the glass of the substrate 10a a plurality of gate and drain bus lines in a matrix shape. In association with the gate and drain bus lines, thin-film transistors (TFTs) 9 are connected to pixel electrodes 8. Consequently, both heat resisting characteristic and flatness are required for the glass substrate employed as the substrate 10a for fabrication of these TFTs 9. The glass substrates 10a and 10b are separated from each other by spacers having a diameter of about several micrometers (xcexcm). Sealed in the gap therebetween is liquid crystal to form a liquid crystal layer 7 so as to form a liquid crystal panel. On each of two outside surfaces, there are arranged polarizing plates 2. For an LCD of a transmission type, a back light layer 11 is provided as shown in FIG. 1. For an LCD of a reflective or reflection type, a polarizer plate of a reflection type is disposed on one of the outside surfaces in place of one of the transmission-type polarizing plates 2. Additionally, electrodes for pen input operation 4 are formed on the opposing glass substrate 10b. This allows use of data input facilities such as a screen input apparatus in which data is inputted to the liquid crystal display when a surface of the apparatus is depressed, for example, by a pen 1.
In addition to the liquid crystal display above, there exists an active matrix LCD of phase-change guest-host (PCGH) mode driven by thin-film transistors. Although the glass substrates of the LCD are the same as those of the TN-type LCD, the liquid crystal includes dichroic dye mixture; moreover, the polarizer plates are dispensed with. As a consequence, when the GH-mode LCD is produced as a reflection-type display, metallic electrodes of aluminum or the like are employed as the pixel electrodes to function also as reflection plates. An LCD having the configuration above has been described, for example, in pages 437 to 440 of the SID 92 Digest entitled xe2x80x9cBright Reflective Multicolor LCDs Addressed by a-Si TFTsxe2x80x9d written by S. Mitsui, Y. Shimada, K. Yamamoto, T. Takamatsu, N. Kimura, S. Kozaki, S. Ogawa, H. Morimoto, M. Matsuura, M. Ishii, K. Awane, and T. Uchida.
There has been known an apparatus to input images in a computer in which an input device is integrated with a display including a screen such that when the screen is directly touched, for example, by a finger, the touched position is presented on the screen.
For example, as shown in FIG. 2, there exists an apparatus including a display 12 and a tablet 13 separated from the display 12, which are fixedly attached onto each other. In this constitution, for example, a liquid crystal display is adopted as the display 12 and a resistive-film-type tablet is used as the tablet in which, for example, small openings are disposed between two resistive films connected to a power source. When the resistive films are brought into contact with each other, an electric current resultantly flowing through the contract point is sensed so as to detect the position of the contact point. In this regard, a reference numeral 14 designates a pen for designating the indication point in FIG. 2. Subsequently, FIG. 3 shows a cross-sectional view of a display with integrated tablet constructed as shown in FIG. 2. The display of FIG. 3 includes a tablet 15, polarizer layers 16 and 17, glass substrates 18 and 19 keeping liquid crystal therebetween, twisted nematic (TN) liquid crystal 20, and a back light layer 21 as a light source.
Conventionally, according to an active matrix LCD in the field of the present invention, a glass substrate having a thickness of about 0.6 mm to about 1.1 mm is utilized for each of the substrates. In consideration of mechanical strength of the glass substrate, it is difficult to further reduce the thickness thereof. In the case where a screen input apparatus such as a pen input device is combined with the LCD of this kind, when a pen of the pen input device is brought into contract with a surface of the LCD to input data such as characters and letters, the thickness of the glass substrate, i.e., the distance between an end point of the pen placed on the surface and an image formed by the liquid crystal is observed as parallax, leading to difficulty in input operation.
On the other hand, the thickness of each film substrate of the LCD is set to about 0.1 mm to remove parallax, when other films are accumulated on the substrate on the pixel electrode side to construct switching elements, the substrate may be warped or cambered by stress of the accumulated thin films because of the reduced thickness of the substrate. In addition, there also exists a problem in which when handling the substrate, the substrate is bent and hence switching elements thus formed are damaged.
Generally, moreover, in a display using the TN liquid crystal, when the gap thickness of liquid crystal is changed, the angle of twist of the liquid crystal is also varied in the pertinent portion, resulting in considerable alteration in transmittivity. Consequently, in the case where a display with integrated tablet is formed using the liquid crystal of TN mode as shown in FIG. 2, when the operator pushes a pen 14 against the tablet 13 to input data in the display, the gap thickness of liquid crystal is altered at the contact point of the pen 14 and in the periphery thereof. Consequently, the value of transmittivity at the position varies from the inherent value thereof in the display operation. This accordingly leads to the problem that quality of the image displayed therein is deteriorated when compared with that of the image in other areas of the screen.
To solve this problem, there has been proposed a method in which, as shown in FIG. 4, a transparent protective layer 23 formed of glass, plastic, or the like is inserted between the tablet 13 and the LCD 12 to prevent pressure of the pen 14 from exerting influence upon the LCD 12. However, when this method is employed, in order to keep the gap thickness of the LCD 12 unchanged, it is necessary to guarantee that the protective layer 23 is not deformed by pressure. For this purpose, a considerably thick and strong protective layer is required to be provided between the tablet 13 and the LCD 12. This inevitably results in of increase in weight and thickness when producing the display with integrated tablet. Additionally, since the end point of the pen 14 is separated from the liquid crystal by several millimeters or more, there also occurs a problem of parallax, namely, the image is displayed at a position displaced from the position indicated by the end point of the pen 14.
It is therefore an object of the present invention to provide an active matrix LCD in which warping of the substrates and damage of switching elements are prevented and parallax between the end point of the pen of the pen input device and the image formed by the liquid crystal is eliminated.
In accordance with the present invention, to achieve the above object, there is provided a liquid crystal display (LCD) with integrated tablet comprising an upper substrate on a viewing side on which electrodes are formed to drive liquid crystal, a lower substrate on an opposing side on which electrodes are formed at positions to drive liquid crystal interposed between the upper substrate and the lower substrate, a liquid crystal of phase-change guest-host (PCGH) mode interposed between the upper substrate and the lower substrate, light illuminating means arranged at a position in a lower portion of the LCD, and tablet means for detecting coordinates disposed at a position in an upper or lower portion of the display not to prevent transmission of light from the light illuminating means.
In accordance with the present invention, there are preferably disposed reflection plates between the upper and lower substrates or at a position in a lower portion of the display, the tablet means for detecting coordinates being disposed at a position in the upper or lower portion of the display not to prevent transmission of reflection light from the reflection plates.
Preferably, in accordance with the present invention, the tablet means for detecting coordinates is formed at a position on the upper or lower substrate of the display not to prevent transmission of light from the light illuminating means, the tablet means being separated from the liquid crystal.
In accordance with the present invention, the tablet means for detecting coordinates is formed at a position on the upper or lower substrate of the display not to prevent transmission of light from the light illuminating means, the tablet means being separated from the liquid crystal.
Moreover, the LCD in accordance with the present invention further includes reflection plates arranged on a surface of the lower substrate, the surface being brought into contact with the liquid crystal. The tablet means is formed at a position between the surface of the lower substrate and the liquid crystal driving electrodes not to prevent transmission of light from the light illuminating means.
The LCD in accordance with the present invention preferably includes reflection plates arranged between the upper and lower substrates, the tablet means being formed between the surface of the upper substrate and the liquid crystal driving electrodes. The tablet means allows transmission of light therethrough.
In accordance with the present invention, the LCD desirably includes reflection plates arranged in a lower portion of the display, the tablet means being formed between the surface of the upper substrate and the liquid crystal driving electrodes. The tablet means allows transmission of light therethrough.
Furthermore, in accordance with the present invention, there is provided an LCD with integrated tablet comprising an upper substrate on a viewing side on which electrodes are formed to drive liquid crystal, a lower substrate on an opposing side on which electrodes are formed at positions to drive liquid crystal interposed between the upper substrate and the lower substrate, the liquid crystal interposed between the upper substrate and the lower substrate, a plurality of pole braces for linking the upper substrate with the lower substrate with a period substantially equivalent to that of pixels of the display, light illuminating means arranged in a lower portion of the display, and tablet means for detecting coordinates disposed at a position in an upper or lower portion of the display not to prevent transmission of light from the light illuminating means.
In accordance with the present invention, there is provided an active matrix LCD comprising a plurality of pixel electrodes arranged in a matrix contour, a substrate on pixel electrode side including pixel driving elements disposed opposing the pixel electrodes, an opposing substrate including electrodes arranged opposing the pixel electrodes, and a liquid crystal layer interposed between the opposing substrate and the pixel electrodes. The substrate on the pixel electrode side includes a glass substrate. The opposing substrate includes a plastic film substrate having a thickness of 0.6 mm or less and is arranged on a viewing side of the display.
Preferably, the display in accordance with the present invention essentially comprises a transmission-type active matrix display of TN mode driven by TFTs.
In accordance with the present invention, the display is preferably a reflection-type display of PHGH mode driven by TFTs.
In accordance with the present invention, the display further includes pen input electrodes.
Preferably, the pixel electrodes of the display in accordance with the present invention include metallic reflection electrodes.
In a liquid crystal display with integrated tablet in accordance with the present invention, a liquid crystal of GH mode is utilized for the LC layer in a display in which when a pen, a finger, or the like is brought into contact with a surface of the display, a position of the surface associated with the contact point is detected on the tablet. Even when the gap thickness of liquid crystal varies due to pressure applied from an end point of the pen or the finger, the change in transmittivity is minimized when compared with that of the conventional TN liquid crystal. Consequently, the deterioration in the quality of displayed image is practically prevented.
Alternatively, a plurality of pole braces or supporting regions are arranged between the upper and lower substrates such that influence from pressure of the end point of the pen or the finger upon the gap thickness is sufficiently reduced. Consequently, the picture quality is not adversely influenced and hence is not deteriorated in practices.
As a result, the protective layer preventing the change in the gap thickness in the prior art can be dispensed with and hence it is possible to minimize thickness and weight of the display. Furthermore, since the substrates keeping liquid crystal therebetween are exposed, the tablet can be formed directly on the substrate. Namely, it is unnecessary to provide the tablet as an independent product.
Moreover, when the film substrate on the viewing side of the operator has a thickness of 0.6 mm or less, when a character or the like is inputted to the display by a pen of a pen input facility, the distance between the end point of the pen and the image displayed by liquid crystal is at most 0.6 mm and hence parallax is rarely recognized by the operator. The thickness of the film substrate is preferably set to 0.2 mm or less. Additionally, since a conventional glass substrate having a thickness of about 0.6 mm to about 1.1 mm is employed for the substrate on the pixel electrode side to constitute switching elements of the active matrix, the camber of the substrate on pixel electrode side is prevented in the manufacturing of switching elements and hence damages damage resulting due to camber is substantially eliminated.